Stacked sheet filter assembly

ABSTRACT

A plurality of flexible metal sheets, each too thin to be selfsupporting, are selectively etched so as to have projections on one surface, and such projections have roughened lateral surfaces. Such sheets are stacked and compressed to form a rigid structure, which is placed in a housing so that entering fluid must pass between the edges of the stacked sheets to reach an outlet. The roughened surfaces and projections trap undesired particles of extremely small size. Housings include threaded locking elements for the stack with passages for equalizing pressures thereon, and grooves or ribs for cooperative locking engagement with the filter elements.

United States Patent Pearson Mar. 14, 1972 [54] STACKED SHEET FILTERASSEMBLY [5 References Cited [72] Inventor: Ronald K. Pearson, 15344East Pentura Drive Hancienda g Cam- 15344 FOREIGN PATENTS ORAPPLICATIONS 846,245 8/ 1952 Germany [22] Filed; Mar, 6, 1969 837,6276/1960 Great Britain Primary Examiner-Frank A. Spear, Jr. [2]] Appl'805048 Attorney-Fulwider, Patton, Rieber, Lee & Utecht Related US.Application Data [57] ABSTRACT A plurality of flexible metal sheets,each too thin to be self- [63] Continuation of Ser. No. 688,938,abandoned, which supporting, are selectively etched so as to haveprojections on cofnmuanofl of 562,043 abandoned, one surface, and suchprojections have roughened lateral surx z f gg of 218,642 faces. Suchsheets are stacked and compressed to form a rigid abandoned structure,which is placed in a housing so that entering fluid must pass betweenthe edges of the stacked sheets to reach an 52 US. Cl ..210/443,210/447, 210/488 "8" The mughened surface? and pmiecfiofls [51] Int, Cl"Bold 25/18 particles of extremely small size. Housings include threaded[58 Field of Search ..210/232, 304, 443,445,446, elements for the Stackwith Passages for equalizing pressures thereon, and grooves or ribs forcooperative locking engagement with the filter elements.

8 Claims, 24 Drawing Figures PATENTEDMAR 14 I972 SHEET 2 0F 5 INVENTOREon/A40 A. 054.254

PATENTEBHAR 14 m2 3. 648 .843

sum 3 or 5 INVENTOR.

' lean/Aw K. flsnesalv PATENTEDHAR 14 m2 3, 648 843 SHEET 0F 5 STACKEDSHEET FILTER ASSEMBLY This application is a continuation of Ser. No.688,938, which is a continuation of Ser. No. 562,043, which is acontinuation-in-part of my copending application, Filter, Ser. No.218,642, filed Aug. 22, 1962, all now abandoned.

The present invention relates to filters and, more particularly, to afilter for removing solid contaminants from a fluid that is utilized bydownstream components.

There is a continuing need for the improvement of filters for theremoval of solid particles from liquid or gaseous media. In recenttimes, this need has become acute in connection with the separating ofparticles of less than 100 micron size from hydraulic fluids, fuels andother fluids utilized in missiles and aircraft.

Heretofore, wire mesh and sintered filters have usually been employedfor the separation of particles smaller than 100 microns. However, thesetypes inherently have disadvantages whereby they give very short servicelines at the level of efficiency indicated by their absolute and nominalratings. For example, the manufacturing processes used inherentlyinvolve a high level of filter element contamination resulting from thesintering or weaving process; the filters have poor resistance tovibration stresses; the filters have an inerently low capacity to resisthigh pressure differentials; the filters have an unsatisfactorytemperature range of operation; and the filter elements cannot becleaned after use and therefore are not reusable.

The foregoing and other disadvantages of previously available filtersare eliminated by my invention.

More specifically, one of the important objects of the invention is toprovide a filter element of unitary or integral onepiece structure thatcan be manufactured and placed into use in an absolutely clean conditionwith no manufacturing contaminant remaining thereon. As a result, whenfilter elements of this type are placed into use, they do not releaseportions of themselves downstream in the effiuent even when subjected toextreme sonic vibration, shock or excessive pressure differentials.

Another object of the invention is to provide a filter utilizing a stackor stacks of such unitary filter elements that are compressively loadedto constitute a rigid column which will stand extremely great pressuredifferentials. Additionally, the stack arrangement of filter elementsprovides an edge of filtration in combination with a depth type offiltration, the latter type of filtration serving to entrap elongatedcontaminants while the edge or surface type of filtration capturesspherical particles or the like.

Yet another object of the invention is to provide a filter that can besold in an absolutely clean condition and which can be recleaned underfield service conditions after having been in service. In thisconnection, the filter of my invention has a removable cartridge and astacking arrangement of filter elements permitting loosening of thecompressive force on the elements whereby every individual element canbe readily be cleaned while the stack is in the loosened condition.Furthermore, individual filter elements of the stack, if found defectiveunder a bubble test, may be removed and replaced whereas with sinteredor wire mesh filters, defects found after bubble testing are brazed orsoldered, thus adding material which can be lost in the effluent.

These and other objects and advantages of the invention will be apparentfrom the following description, when taken in conjunction with theannexed drawings.

FIG. 1 is a perspective view of a filter assembly incorporating theinvention, the assembly being longitudinally sectioned on a diametralplane to disclose details of interior construction;

FIG. 2 is a perspective view of the filter cartridge utilized in theassembly of FIG. 1;

FIG. 3 is a transverse sectional view of the filter assembly taken onthe line 33 in FIG. 1;

FIG. 4 is a partial plane view of the area 4 of FIG. 3, on an enlargedscale, to show details of the configuration of one side ofa filterelement;

FIG. 5 IS A sectional view on the line 55 of FIG. 4, on a furtherenlarged scale;

FIG. 6 is a plan view of an alternative configuration of filter elementfor use in the assembly of FIG. 1;

FIG. 7 is an axial sectional view of an alternative embodiment of filterassembly;

FIG. 8 is a transverse sectional view on the line 8-8 of FIG.

FIG. 8a is a partial plan view of one surface of one of the filterelements of the assembly of FIG. 7;

FIG. 9 is a longitudinal sectional view of a radiator type filterassembly embodying the invention;

FIG. 10 is a sectional view taken on the line 10-10 of FIG.

FIG. 11 is a partial plan view of the area 11 of FIG. 10, on an enlargedscale, showing the configuration of one side of a filter element;

FIG. 12 is an axial sectional view of an alternative embodiment of anin-line filter assembly;

FIG. 13 is a transverse sectional view taken on the line 13- 13 of FIG.12, showing the dual inlet arrangement for the influent;

FIG. 14 is a sectional view on the line 14- 14 of FIG. 12;

FIG. 15 is a partial plan view of the area 15 of FIG. 14, on an enlargedscale;

FIG. 16 is a sectional view on the line l6--16 of FIG. 14;

FIG. 17 is a transverse sectional view of a filter cartridge containinganother configuration of filter element;

FIG. 18 is a partial plan view of an inner area of thin sheet metalhaving a resist pattern thereon to illustrate a step in the process ofmaking a filter element;

FIG. 19 is a view of the resist pattern on the other side of sheet metalpiece shown in FIG. 18;

FIG. 20 is a sectional view on the line 2020 OF FIG. 18, schematicallyindicating another step in the process of etching filter elements;

FIG. 21 is a partial plan view of another embodiment of a filter elementof my invention;

FIG. 22 is an enlarged fragmentary plan view of the filter element ofFIG. 21; and

FIG. 23 is a partial plan view of a still further filter element of myinvention.

FIG. 1 shows a T-type filter assembly 20 in which is mounted a filtercartridge 21, such as is seen in FIG. 2. This assembly includes agenerally cylindrical housing 22 which may be formed integrally with anupper end wall 23 closing the upper end of the housing. The housingdefines a generally cylindrical chamber 24 having a smooth land 25 atits lower end adapted to slidably receive a cylindrical cage 26 of thecartridge 21. The upper end or roof of the chamber 24 has a downwardlyprotruding index pin 27 adapted to seat in a blind index bore 28 formedin the upper face of an integral flange 29 of the upper end of the cage26. The cartridge 21 is thus held in predetermined angular relationshipwithin the housing 22. At its lower end, the chamber 24 is internallythreaded, as indicated at 30, to threadably receive a locking disc 3!1by means of which the filter cartridge is securely held against the roofof the housing 22. Beneath the internal threads 30, the chamber 24 isformed with a smooth counterbore 32 to slidably receive a cylindricalboss portion of a cap 33 that closes the lower end of the housing. Thiscap may be held in place by a plurality of bolts 34, or other suitablefastening means, to seal the lower end of the housing 22, The lower endof the chamber is bevelled, as indicated at 35, to receive an O- ring 36that is mounted around the boss of the cap 33.

The filter cartridge 21 defines an annulus with the housing 22 to whichthe fluid to be filtered is introduced through an inlet port 37 andintermediate passage 38. The cartridge 21 contains a coaxially arrangedstack of ring shaped filter discs 40 defining a hollow core for thefilter cartridge. Thus, the fluid passes radially inwardly from theannulus, between discs 40, thereafter to be passed through the hollowcore of the cartridge and exhausted from an outlet port 41 of thehousing. To

insure that none of the fluid bypasses the filter cartridge 21, acircular groove 42 is formed in the upper end flange 29 of the filtercage 26 to hold an O-ring 43.

Each of the filter elements is made of an impervious material,preferably sheet metal that has been etched, cut, rolled, coined orotherwise formed. For critical applications where it is desired, forexample, to make a filter having an absolute rating of 25 microns, thefilter elements preferably comprise stainless steel sheet which iscompletely formed by etching.

More specifically, let it be assumed that the filter has an absoluterating of microns. Each of the identical filter discs 40 is them madefrom stainless steel sheet by etching the sheet into the ring likeconfiguration shown, and to leave on one surface of the disc an array orpattern of protrusions 40a integrally with an impervious base portion40b. The stainless steel sheet from which the discs 40 are etched has anoriginal thickness of 0,002 inch and is partially etched on one face toa depth of 0.001 inch whereby the protrusions 40a extend 0.00! inchabove the base section 40b. The discs 40 may be etched with unbrokeninner and outer peripheral edges, if desired, but in this instance, inorder to increase the edge filtration area, the discs have been etchedto leave a crenelated outer edge 40c and may also have an innercrenelated edge 40d. An alternative inner end outer edge configurationfor another form of disc 40' is shown in FIG. 6 having sawtooth innerand outer edges 40d and 40c'respectively, etched in the disc.

As is shown in FIG. 5, the discs 40 are stacked one on top of the otherwith the protrusions 40a of one disc in engagement with the smoothunetched surface of another disc 40 so that there is a gap at both theinner and outer edges of an adjacent pair of discs of 0.001 inch.Accordingly, when a stack of the discs 40 is compressively and coaxiallyheld, as in the cartridge 21, edge filtration occurs at the outer edgeof the discs 40 so that particles exceeding 25 microns in diameter arekept from passing radially inwardly through the stack. Inwardly of theouter surface of the stack, a depth type of filtration occurs due to thepresence of the protrusions 40a which will capture such elongatedparticles, having a diameter of 25 microns or smaller which have managedto pass inwardly of the outer surface of the stack. Such elongatedparticles, as for example, cotton linters, will not be capable offollowing the sinuous path between the closely spaced protrusions 40aand therefore will be caught.

As is shown in FIG. 4, the protrusions 40a are Y-shaped and are closelyspaced together. More specifically, each protrusion 40a has the arms ofthe Y opening radially outwardly of the disc with the stem of the Ydisposed substantially in a radial direction of the disc. A stagnationcavity 46 is thus defined by the pair of arms of each Y-shapedprotrusion 40a which will capture a substantial part of all sphericaland fibrous particles smaller than 25 microns which pass the edgefiltration action of the stack of discs. It should also be noted thatthe gap between the stem portions of an adjacent pair of Y-shapedprotrusions 40a is interrupted by a stagnation cavity 46 of anotherprotrusion 40a positioned behind the adjacent pair of protrusions. Forexample, in FIG. 4 an adjacent pair of protrusions x and y have the gapbetween their stem portions interrupted by the stagnation cavity ofanother protrusion. With this arrangement, not only is a very sinuouspath defined for the entrapment of elongated particles, but theclearance between protrusions 40a can be held to a very small value toarrest the passage of such particles, smaller then 25 microns, as maynot be entrapped in the stagnation cavities 46.

The discs 40 have an outer diameter to be slidably receivable within thecage 26 and an innner diameter corresponding to the diameter of theeffluent opening through the flange 20 in the upper end of the cage.When the cartridge 21 is assembled, all of the discs 40 are oriented inthe manner shown in FIG. 5, i.e., with the protrusions 40a of each discabutting the underside or unetched surface of the disc 40 just above oradjacent. For a 25-micron filter, 400 of the discs 40 are utilized foreach inch of filter, measured axially of the stack of filters discs. Therequired number of discs are placed within the cage 26 to be seated, atone end of the stack, on the flange 29 of the upper end of the cage. Atintervals of about 1 inch, rigid washers 65 are placed in the stack ofdiscs to aid in holding the discs against turning when torque is appliedat one end of the stack to compress it into a rigid column and, also, toprevent the disc tilting out of planes normal to the axis of the stack,which could occur due to an accumulation of tolerances of the discs oraccumulation of slightly bent discs.

The lower end of the case 26 is tapped to receive a nut 49 to clamp thestack of discs 40 against the flange 29. The discs 40, before clamping,may not be perfectly flat and the loosely contained stack of discs andwashers will have slack to occupy an over-all length greater than thefinished length. After tightening of the nut 49, all slack between discswill be taken up and there will be approximately 500 discs per inch andthe entire stack has the characteristics of a relatively incompressibleloaded structural column. In this connection, the close spacing of theprotrusions 40a is important, and the pattern of distribution of theprotrusions, in order to insure that a large proportion of protrusionswill not penetrate into or bend the surface of another disc. Care shouldbe taken to insure that a majority of the protrusions of a disc havebearing contact with areas of an adjacent disc that are also the basesof protrusions of the adjacent disc to define columnar areas through thesuperposed protrusions or superposed areas of protrusions.

After the nut 49 has been tightened, a lock nut 50 is screwed onto thetapped lower end or skirt of the case 26. The cartridge 21 is then readyfor placement within the housing 22 to be held in place by the nut 31that bears against the lower end of the cage 26.

As is shown in FIG. 2, the wall of the cage 26 is cut away between thelower end skirt and the upper end of the cage leaving fourlongitudinally extending bars 51, 52, 53, and 54 between which the outeredges 40c of the discs 40 are exposed, as the edge filtration area ofthe filter cartridge. The opening between the bars 51 and 52 is ofshorter length than the other openings to provide a deflector 55.Because of the index pin 27, the cartridge 21 is set within the housing22 in a predetermined angular relationship whereby the deflector 55 ispositioned opposite the passage 38 from the inlet 37 of the housing 22.Thus as the fluid to be filtered enters the housing 22 and leaves thepassage 38, the particles therein do not impinge on the edges of thediscs 40 behind the deflector 44. Accordingly, wear of the outer edgesof this group of discs 40 is avoided and the particulate matter withinthe fluid is uniformly dispersed throughout the annulus defined aroundthe filter cartridge.

To counterbalance the fluid pressure exerted on the holding nuts, asystem of pressure relief ports is provided in the nuts 49, 50 and 31.The nut 49 has a plurality of ports 60 extending from the upper surfaceat the outer edge of the nut downwardly and radially inwardly to openinto the undersurface of the nut. The upper surface of the nut 50 isformed with a shallow cylindrical cavity 61 and the spanner wrench holes62 of the nut 50 extend through the nut so that fluid reaching thecavity 61 from the ports 60 can pass through the nut 50. Similarly, thenut 31 has through spanner holes 63 to pass fluid to the space betweenthe nut 31 and the heavy cap 32 for the housing 22. In this manner,pressures tend to be equalized on the nut 31, nut 50 and nut 49.

In FIG. 7, the invention is embodied in an inline filter assembly 70. Inthis assembly, a tubular housing 71 is formed with an interior integralpartition 72. On the downstream side of the partition, an annular recess73 is formed to receive a ring 74 that is one end of a cage to contain astack of filter discs 75. The other end of this cage comprises a ring 76disposed in a plane diametrically to the axis of the stack of filterdiscs 72 and interconnected to the ring 74 by a plurality of ribs 77.

The discs 75 may also be made of a very thin sheet metal which is firstdie formed into conical configuration and then etched to leave thering-like plan configuration shown, with inner and outer edges 75a and75b, respectively. Then, one

face of the disc is etched to the desired depth, leaving circularprotrusions 75c integral with an imperforate base portion 75d. Forexample, it it is desired to have a filter with an absolute rating of 25microns, the filter discs are made from 0.002-inch sheet and one face isetched to leave the protrusions 75c extending 0.001 inch above the basesection 75d. With respect to FIGS. 7, 8, and 8a, it will, of course, beappreciated that the thickness of the filter discs and the apparent areaand height of the protrusions 75c and the spacing between theprotrusions have been greatly exaggerated for clarity of illustration,just as in the case of the other filter elements illustrated in thedrawings. 7

The filter discs 75 are arranged in a stack as shown in FIG. 7 so thatthe etched surface of one disc abuts the unetched surface of an adjacentdisc. The stack of filter discs 75 is thereafter compressed to achievethe desired structural column effect and to achieve the desired gap of0.001 inch between outer edges 75d for edge filtration.

The downstream side of the partition 72 is formed with a frusto-conicalnose 80 to seat the concave face of the disc 75 at that end of the stackof the discs. The cage for the filter discs 75 is inserted first withthe ring 74 in place on the shoulder 73. Thereafter, the loose stack ofdiscs 75 is inserted through the opening in the ring 76 and the stack isthus held in coaxial alignment by the cage. The downstream end of thehousing 71 is interiorly tapped, as indicated at 81, to threadly receivea downstream end fitting 82, formed with a circumferential groove 83 toseat an O-ring 84 to effect a fluid seal between the fitting and thehousing. The end fitting 82, at its inner end, has a flat end face 85adapted to abut the ring 76 of the disc retaining cage. Within the flatend 84, the fitting 82 is formed with a frusto-conical seat 86 to seatthe convex face of the disc 75 at that end of the stack of filter discs.Tightening of the end fitting 82 causes compression of the stack offilter discs 75 against the disc seat formed on the nose of thepartition 72. In this connection, the annular recess 73 providesclearance to permit full or complete compression of the stack of filterdiscs. The end fitting 83 is itself exteriorly threaded to receive alock nut 87 that can be run up against the corresponding end of thehousing 71 to retain the end fitting 82 in clamping position. The endfitting 82 has an axially extending outlet port 88 communicating with anoutlet port adapter 89 that is threadedly received in the end fitting.An O-ring 90 is retained between the adapter 89 and the tapped bore ofthe end fitting 82 to effect a fluid seal.

The partition 72 is formed with a plurality of spaced passages 91 toreceive the influent fluid from an inlet end fitting 92 threaded to theinlet end of the housing 71, as indicated at 93, The inlet end fitting92, at its inner end, is formed with a circumferential groove 94 to seatan O-ring 95 to effect a fluid seal between the housing and the inletend fitting. The inlet end fitting also has an axially extending inlet96 that is tapped to receive an inlet port adapter 97. An O-ring 98 isretained under the head of the adapter 97 to effect a fluid seal betweenthe adapter and the fitting 92.

In the operation of the filter assembly 70, the influent enters thefitting 92 and is distributed by the ports 91 of the partition 72 intothe annular spaced defined between the stack of filter elements 75 andthe wall of the housing 71. Edge filtration of particulate matter occurson the outer edges of the filter discs 75, the edge spacing determiningthe absolute rating of the filter assembly 70. The fluid then passesinwardly to the hollow core of the stack of filter discs in thefrusto-conical paths dictated by the configuration of the filter discs75, and depth filtration occurs whereby elongated particles of smallerdiameter than the edge gap become entrapped by the protrusions 75c. Thefiltered effluent is then passed outwardly from the hollow core of thestack of filter discs 75 through the bore 88 in the outlet fitting 82.Thus, the filtering action of the filter assembly 70 is very much likethat in the filter assembly 20. However, a lesser pressure drop will beencountered with the filter assembly 70 due to the frusto-conicalconfiguration of the filter discs, and the corresponding passageconfiguration,

which gives an axial component to the flow of fluid through the filter.

In FIG. 9, the invention is embodied in a radiator type filter assembly110. The filter housing has a body 111 whose lower end is sealed by agasket 112 held in place beneath a bottom cap 113 that is retained by aplurality of suitable bolts or other fasteners 114. The upper end of thebody 111 has its edge sealed by another gasket 112, beneath a removablecover plate 115 that is retained by a plurality of bolts 114 also. Aninlet port 116 is provided in one end wall of the body 111 and in theopposite end wall there in an outlet port 117.

The filter assembly has a stack of identical filter elements 120. As isshown in FIG. 10, each of these elements is an elongated rectangularlyshaped strip, preferably of stainless steel, that has been etched intothe rectangular shape shown and also etched to produce front and rearedge spaced compression pads 120d and Y-shaped protrusions 120a shown inan exaggerated scale in FIG. 1 1. As in the case of the filter elements40 of the filter assembly 20 of FIG. 1, for a 25-micron rating, each ofthe filter elements 120 has an over-all thickness of 0.002 inch, beingthe total of a base section 12% thickness of 0.001 inch and a height ofthe protrusions 120a, above the base section, of another 0.001 inch. Thegap between forward edges 1200 of an adjacent pair of filter elements120 is thus 0.001 inch in the spaces between pads 120d whereby allparticles above 25 microns in size are excluded from the radiator bankof filter elements. The Y-shaped protrusions 1200 are arranged in thesame type of pattern is employed in the filter discs 40 of FIG. 3, sothat a stagnation cavity 121 of each rearward line of protrusions isbehind the gap between front edge pads 120d or between an adjacent pairof protrusions immediately in front of the stagnation cavity. Also, thespacing between adjacent protrusions 1200 is preferably held to 0.001inch, i.e., the space between opposed arms of an adjacent pair of Y's.The arms and stem of each Y may have a width on the order of 0.003 inchand each Y may have an over-all length of 0.030 inch and an over-allwidth of 0.020 inch.

As is shown in FIG. 10, the bank of filter elements 120 is held in placewithin the body 111 by a pair of vertically extending slots 123 formedin opposite side walls of the body. If desired, a sealing gasket or thelike may be employed within each groove 123 to prevent unfiltered fluidbeing passed around the ends of the bank of filter elements 120.However, such seal means may be eliminated if the filter elements 120are of a length to give a press fit within the slots 123, or longer thanthe span between floors of the grooves 123 by a distance of 0.001 inch.A clamping bar 124 is seated on top of the bank of filter elements 120and is also of a length to have its ends received within the grooves123. The opposite ends of the bar 124 may be provided with a fluid sealmeans or may also have a very close fit within the slots with aclearance tolerance no greater, over-all, than the rating of the filter.

When the cover plate is fastened down the clamping bar 124, it fullycompresses the bank of filter elements 120, eliminating all slack sothat a solid vertical column is achieved with approximately 500 of thefilter elements within each inch of height of the radiator bank. Forholding the bank of filter elements 120 against the operatingdifferential pressure of the filter, a pair of support columns 125 abutsthe downstream side of the bank of filter elements. As is shown in FIG.10, these vertically extending columns 125 preferably have flat bearingsurfaces to contact the rear side of the bank of filter elements.Referring to FIG. 9, it can be seen that each column at its lower endhas an integrally formed pin 126, that is seated within a complementarysocket formed in the upper surface of the bottom plate 113. At its upperend, each column 125 has an integrally formed cylindrical flange 127that is receivable within a complementary pocket 128 formed in the lowerface of the top cover 115. A spring 129 is seated within the cylindricalflange 127 and pocket 128 to bias each column 125 downwardly into asecure seat of the pin 126 on the lower end into its socket. Thisarrangement allows clearance at a shoulder 130 defined between thecollar 137 and the upper end of the column 125 to insure that the heightof the columns 125 will not prevent completely clamping the cover 115down onto the bar 124, to fully compress the stack, and, also, to insurethat the gasket 112 at the upper end of the body 11 is tightly clampedin place.

In FIG. 12, the invention is embodied in another configuration ofin-line filter assembly 130. A cylindrical housing 131 at one end has afrustoconical shaped dome 132 that develops into an inlet port 133. Thisdome is interiorly tapped to receive an inlet pipe 134 coaxially withthe housing the other end of the housing 131 is formed with an exteriorcircumferentially extending flange 135 on which a base plate 136 of aremovable filter cartridge is seated. A suitable O-ring 137 is mountedbetween the flange 135 and base plate 136. The base plate 136, in turn,seats a mounting flange 138 of a cap member 139 which has a tappedoutlet port 140 to receive an outlet pipe 141. An O-ring 142 is mountedbetween abutting faces of the mounting flange 138 and base plate 136 toeffect a fluid seal between these parts. The flange 135, base plate 136and mounting flange 138 are formed with alignable bores for thereception of suitable bolt fasteners 143 to hold these parts together.

The filter cartridge is carried on the base plate 136 and can be removedalong with the base plate after the bolts 143 and cover member 139 havebeen removed from the housing 131. The cartridge includes a plurality ofidentical filter discs 145, a plurality of longitudinally extending tierods 146 anchored at one end in the base plate 136, and at the other endthreadedly engaged with a pressure plate 147. Also included in thefilter cartridge are a plate 148, that is retained by the tie rods 146,and a pressure screw 149, threadedly engaged with the plate 147 andacting to clamp the filter discs 145 between the plate 148 and the baseplate 136.

More specifically, the filter discs 145, for a ZS-micron filter, aremade from 0.002-inch stainless steel sheet that is etched in the planview configuration shown in FIG. 14. Each disc is generally circular inshape having a central opening 145a and a saw-toothed outer edge 1451:.This outer edge is not continuous but at positions spaced 90 apart isformed with semicircular notches 145c adapted to receive the tie rods146. The filter discs 145 are thus indexed into a desired angularorientation, relative to each other and to the base plate 136. Each ofthe filter discs 145 is formed with four circularly spaced apartarcuately shaped grooves or openings 145d and the base plate 136 isformed with openings 150 of the same configuration and similarly spacedapart.

After the filter discs 145 have been etched to the plan configurationjust described, they are etched to produce the surface configurationschematically shown in FIG. 14. Thus, one surface of each disc is etchedto a depth of 0.001 inch to leave the illustrated pattern of Y-shapedprotrusions having an altitude of 0.001 inch above a base section145fofa thickness of 0.001 inch and, also, leaving four elongated padsof pad areas 145g extending radially from the center hold 1450. In orderwords, the pad areas 145g and the Y-shaped protrusions 145s are unetchedwhile the balance of the surface of the disc is etched to a depth of0.001 of an inch. The Y-shaped protru sions are arranged in accordancewith the scheme previously described.

In the filter assembly 130, the influent enters the inlet port 133 andenters the stack of filter elements 145 both from the annular spacebetween the stack of filter elements and the wall of the housing 131 andalso from within the hollow core defined by the inner edges 145a of thestack of filter discs. As is shown in FIG. 13, the plate 148 is formedwith a plurality of radially extending passages 152 having their innerends in communication with an axially disposed orifice 153 having thesame diameter as the diameter of the filter openings 145a andcommunicating with the hollow core defined by the holes 145a.Accordingly, the influent passes radially inwardly from the outer edgeof the stack of filter discs 145 and also passes radially outwardly fromthe hollow core of the stack. The filtered effluent, i.e., the fluid inthe arcuate passages 145d is then drawn axially from the filter stackthrough the base plate passages 150, the outlet port and pipe 141.

Referring to FIG. 14, it will be noted that in each of the quadrants orseparate areas of the filter discs 145, the Y- shaped protrusions e,positioned radially outwardly from the arcuate openings 145d arearranged to dispose their stagnation cavities 155 facing outwardly. Ineach quadrant of the filter discs 145, those Y-shaped protrusions 145::that are radially inwardly from the arcuate openings 145d are orientedwith their stagnation cavities facing radially inwardly. In connectionwith the scale of the drawings, it will be appreciated again that therelative size of the protrusions is greatly exaggerated for clarity ofillustration.

As with the previously described filter assemblies, so too in the filterassembly 130, the filter discs 145 are stacked with the etched face ofone disc in abutment with the smooth unetched face of an adjacent disc.These congruent discs are assembled with each of the discs being indexedby the tie rods 146 whereby the pads 145g, protrusions 145e and theopenings 145d are congruently superposed. The openings 145d registerwith the openings 150 in the base plate 136 while the hollow coredefined by the holes 1450 registers with the port 153 of the plate 148.

As is shown in FIG. 13, the tie rods 146 extend through suitably locatedopenings in the plate 148, these openings having a sliding fit on thetie rods. The plate 147 is also formed with openings to slidably receivethe tie rods 146 and is held in place on the tie rods by cap nuts 157threadedly engaging the ends of the tie rods. The clamping screw 149 isthreadedly engaged with a tapped bore in the center of the clampingplate 147 and the inner end of the screw bears against the center of theplate 148 to remove all slack and fully compress the stack of filterdiscs between the plate 148 and the base plate 136. Once again, assuminga 25-micron rating for the filter, when the stack of filter discs 145 isfully compressed there are substantially 500 of the discs per inch ofaxial length of the stack. In this connection, it is important to note,as is shown in FIG. 16, that the pads 145g are protrusions l45e areexactly superposed so that when the stack is fully clamped, the stackhas rigidity and structural column characteristics like a thickwalledtube.

FIG. 17 illustrates another embodiment of the invention that is adaptedto prevent placing any filter disc into a cartridge in a reverseposition, i.e., with the protrusions of the filter disc abutting theprotrusions or etched side of another filter disc. In this instance,there is a filter cartridge or cage 161 generally similar in overallconfiguration to the cage 26 shown in FIG. 2, having a spaced pair oflongitudinally extending bars 162 and 163 extending between oppositeends of the cage. While bars 162 and 163 are relatively distantlyspaced, another pair of relatively small cross-sectional area bars 164and 165 are relatively closely spaced to define a keyway 166therebetween. This keyway receives a compression pad area 167 thatprotrudes radially outwardly from a filter disc 168 and the disc has aplurality of integral protrusions 169 on one surface, in the areabetween outer edge 168a and inner edge 16812 of the ringlike disc.

It will be noted that the outer edge 168a of the filter disc is formedwith a substantially semicircular notch 168C that is located generallyoppositely to the compression pad 167 but offset from a diameter whichwould intercept the compression pad. An index rod 170 is mounted in thefilter cage 161 in a corresponding position in the gap between the bars162 and 163 to register with the indexing notch 168 of the filterelement. If the filter disc is reversed, it cannot be received into thecartridge because the indexing notch 1680 would not register with theindex rod 170 even if the compression pad 167 were positioned within thekeyway 166. Thus, there is no possibility that any single filter disc168 can be inserted into the cartridge in reversed position and thedesired edge gap between discs will always be maintained since there isnot possibility of the protrusions 169 of one disc seating onprotrusions 169 of an adjacent disc.

As has already been indicated, it is highly preferable that the filterelements be made by etching the filter element from a thin sheet ofmetal, so as to provide an absolutely clean filter media, no part ofwhich can be displaced to be lost downstream in the filter effluent.This process may be carried out as indicated in FIGS. 18, 19 and 20which show, by way of example, steps in the formation of the filter disc168 shown in FIG. 17.

FIG. 18 shows a corner area of a thin sheet of metal 175 which may beassumed to have an original thickness of 0.002 inch. For convenience,that side of the sheet of metal 175 shown in FIG. 18 will be referred toas the upper side, corresponding to what may be termed the upper side ofthe filter disc 168 depicted in FIG. 17. The reverse side of the sheetmetal 175 is shown in FIG. 19. In FIGS. 18 and 19, the shaded areasrepresent a suitable etchant resist material which may be applied bysilk screen or photographic process to block out or protect those areasof the sheet which are to remain unetched. Thus, in FIG. 17, thecircular raised protrusions 169 and the compression pad area 167 are theonly unetched areas of the upper side of the filter disc 168. The samereference numerals are used in FIG. 18 to represent corresponding areasof the sheet 175 which are covered with resist material so as not to beremoved from the upper surface of the sheet by the etchant. In similarfashion, in FIG. 18, the reference numerals 168a and 168b show edges ofmasked areas of the sheet 175 corresponding to outer and inner edges168a and 168b of the filter disc 168 shown in FIG. 17. On the bottom orreverse side of the sheet 175, as shown in FIG. 19, the entire surfaceof the sheet is masked by the resist except for the outer edge 168a,including the indexing notch 168C and compression pad 167, and thecompletely circular inner edge 168b.

It will be observed that the outlines of the several filter elementsmarked on the upper surface in FIG. 18 are in mirror image relationshipto the outlines of the filter elements marked on the bottom surface inFIG. 19, and the patterns on the opposite sides of the sheet are ofcourse exactly superimposed. Accordingly, when the resist-coated sheet175 is immersed in an etchant, the exposed areas of the sheet areattached by the etchant simultaneously on both sides of the sheet. Thisis indicated schematically in FIG. 20 where it will be seen that metalhas been removed between the masked protrusions 169, around the outeredge 168a, and around the inner edge 168b, the etched areas beingattacked simultaneously from opposite sides of the sheet. It is to beunderstood that in the representation of FIG. 20, the etchant has notyet fully penetrated but the etchant, in the given example of a sheet of0.002 inch thickness, is of sufficient strength to penetrate to a depthof 0.001 inch whereby each of the filter elements 168 will be fullysevered from the sheet 175 along the edges 168a and 168b, and onesurface only of each filter element will have the metal removed betweenthe protrusions 169a on one side ofthe sheet only.

In the event filter elements of the configuration of the element 75 ofFIG. 8 are desired, a sheet of metal like the sheet 175 in FIGS. 18, 19and 20 can first be frustoconically dimpled by forming dies and theresist then applied to etch the filter elements with their protrusionsfrom the preformed sheet. Alternatively, flat filter elements may bemade from a thin sheet metal by first piercing the blanks of desiredplan configuration from the sheet with piercing dies, and thereafterapplying a resist to the filter element blanks to accomplish the removalof metal from one surface in order to leave the desired configurationand distribution of protrusions. However, etching to sever the filterdisc blank or fully formed disc from the sheet is highly preferablesince it does not involve the possibility of producing slivers and chipsand tears of metal, such as could result from piercing the sheet withpiercing dies.

FIGS. 21-23 illustrate filter elements having etch patterns uniquelyshaped to cause fluid passing through a filter to be subjected to aswirl, and causing particles to be carried into and lodged in crevices.Referring to FIGS. 21 and 22, a thin metallic ring 181 is etched toprovide curved channels 182 through which fluid passes to the interiorof the ring.

As best seen in FIG. 22, the etched channel 182 in the arrangement shownhas an unbroken curved wall 183, and a curved wall 184 that has afolded-back portion 185 extending into the channel and toward the outeredge of the ring.

With a stack of filter elements of this construction, fluid forcedthrough the channels is subjected to a swirl, or centrifugal force,which tends to carry particles into the crevices formed between thewalls 184 and the extensions 185.

FIG. 23 illustrates a ring 186 with an etch pattern which serves thesame purpose as for the element of FIGS. 21 and 22. The channels 187 inFIG. 23 are shaped so that one wall 188 thereof is provided with anumber of spaced reentrant portions 189.

FIGS- it should be observed that the etching causes the floors and wallsof the channels to be roughened. Hence, the floor and wall surfacesthemselves serve to trap particles which would pass through if thesesurfaces were smooth. The degree of roughness can be controlled asdesired, and may be such that the surfaces are relatively jagged toenhance trapping of particles to be filtered out of the fluid.

From the foregoing description it will be apparent that the filter mediaof my invention may be embodied in a wide variety of configurations.Additionally, as the filter media is of integral or unitaryconstruction, there is no possibility of. media migration, i.e., removaland displacement of portions of the filter media which can be passedinto the effluent. F urthermore, as no foreign matter is manufacturedinto the filter ele ment, as is the case with sintered or wire mesh orscreen filter media, there is no possibility of such foreign matterbeing released into the effluent as a result of vibration of the like.

With the present invention, a filter cartridge can be subjected to abubble test prior to installation of a filter assembly. Then if anydefective surface area be found, the stack of filter elements may beloosened and the individual defective filter discs or layers may beremoved and replaced by other filter discs and the cartridge may then bereassembled. This procedure completely eliminates the necessity for anybracing, as is common with screen or sintered types of filters, in whichbrazing to close unacceptable voids results in the addition of foreignmatter which can be lost in the effluent and also reduces the filtrationarea.

The filter of my invention may be more effectively cleaned by sonic ormechanical vibration as such vibration will not result in the removaland displacement of any portion of the filter media. Furthermore, as afilter cartridge may be removed from the filter assembly after a periodof use and loosened to effect a spacing between filter elements, it isnow possible to clean the depth filtration space of the filter as wellas the edge filtration area.

While several embodiments of my invention have been hereinabovedescribed in detail, it is to be understood that I do not mean to belimited to the specific details of construction set forth, but only bythe spirit and scope of the following claims.

I claim:

1. A stack of substantially identical, very thin, flexible metal sheets,each sheet having portions etched from one surface thereof to leave aplurality of spaced projections in a prescribed pattern integral with animperforate base section of the sheet, said base section and the lateralsurfaces of the upstanding portions of said projections having minuterough surfaces, each sheet also having an etch-roughened peripheral edgesurface;

a housing for said stack;

and means for compressing said stack in said housing to form a rigidstack of said flexible sheets resistant to vibration and with saidpattern of projections and said rough surfaces arranged to trapparticles in fluids that flow between said sheets.

2. A filter as defined in claim 1, wherein each sheet has a centralopening therein, and wherein the edge surface of the sheet around saidopening is etch-roughened.

3. A filter as defined in claim 1, wherein said housing has opposedgrooves and each sheet is a rectangular element nesting at its ends insaid grooves;

a pair of rigid rod-like members supported in said housing and abuttingone side of the stack;

and means to introduce fluid into said housing on the side of the stackopposite said rods.

4. A filter as defined in claim 1, wherein each sheet has a tab and anotch along its periphery which are angularly spaced so as not to bediametrically opposed, and wherein said housing has a longitudinal riband a longitudinal groove for mating with the respective notches andtabs of said sheets.

5. A filter as defined in claim 4, wherein said rib is formed of asecond longitudinal groove in said housing confronting the notches insaid sheets and an index rod extending through the opening defined bysaid second longitudinal groove and said confronting notches.

6. A filter comprising:

a stack of substantially identical flexible metal sheets, each sheetbeing etch-roughened on one surface and with a pattern of projections onsaid one surface;

a housing for said stack;

a body having inlet and outlet ports at one end to admit fluid into saidbody and through which fluid passes out of said body;

means positioning said housing in said body with one end of the stackadjacent said one end of said body, said housing having openings thereinto permit fluid entering said body to pass laterally between said sheetsinto the center openings thereof, said body having a passageway throughwhich fluid entering said center openings passes out of said outletport;

a pair of rigid washers at each end of said stack, one of said path of afluid containing particles to be trapped, said cartridge comprising:

a stack of substantially identical flexible metal sheets, each sheethaving one roughened surface and a plurality of spaced projections in aprescribed pattern integral with said surface, the lateral surfaceportions of said projections being minutely roughened;

a housing for said stack;

means for compressing said sheets in said housing to make a rigid stack,whereby to pennit said stack to resist vibration, and whereby saidpattern of projections and said roughened surfaces serve to trapparticles in a fluid that flows between said sheets.

8. A filter as defined in claim 7, wherein said means for compressingsaid sheets includes a member supported in said housing and havingpassages interconnecting its opposite surfaces for pressureequalization.

UNITED STATES PATENT OFFICE CERTIFICATE o5 CORRECTION Patent No. 48,843bated March 14, 1972 Inventofla) Ronald earson It is certified that:error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

COLUMN 1, Line 18, change "give" to -have--; same line, change "lines"to --lives--; line 23, change "inerently" to -inherently; line 55, after"can" delete "be"; line 73, change "plane" to -plan-.

COLUMN 2, Line 2 9, after "sheet" insert -ofline 57, change "311" to-3l--; line 64, after "22" change to COLUMN 3, Line 18, change "0,002 to--o.oo2--; line 74, change "filters" to --filter--.

COLUMN 4, Line 6, change "disc" to --discs-; line 27, change "onto" to--into--q COLUMN 5, Line 3, change "it" .(first occurrence) to -if-.

COLUMN 6, Line 29, change "is" to --as line 44, after "around" delete"the"; line 75, change "137" to --l27-.

COLUMN 7, Line 56, change "order" to other--. I

COLUMN 8, Line 39, change "are" (first occurrence) to -and. 1 I V COLUMN9, Line 14, after "sheet" insert '-of-.

CLAIM 1 (Column 10) after line 55, insert first three lines of claim asfollows:

A filter to be placed in the path of a fluid containing particles to betrapped, said filter comprising:.

Signed and sealed this 26th day of September 1972.

(SEAL) Attest:

EDWARUMQFLETCHERJ'R. ROBERT GOTISCHALK Attestlng Officer Commissioner ofPatent

1. A stack of substantially identical, very thin, flexible metal sheets,each sheet having portions etched from one surface thereof to leave aplurality of spaced projections in a prescribed pattern integral with animperforate base section of the sheet, said base section and the lateralsurfaces of the upstanding portions of said projections having minuterough surfaces, each sheet also having an etch-roughened peripheral edgesurface; a housing for said stack; and means for compressing said stackin said housing to form a rigid stack of said flexible sheets resistantto vibration and with said pattern of projections and said roughsurfaces arranged to trap particles in fluids that flow between saidsheets.
 2. A filter as defined in claim 1, wherein each sheet has acentral opening therein, and wherein the edge surface of the sheetaround said opening is etch-roughened. 3 A filter as defined in claim 1,wherein said housing has opposed grooves and each sheet is a rectangularelement nesting at its ends in said grooves; a pair of rigid rod-likemembers supported in said housing and abutting one side of the stack;and means to introduce fluid into said housing on the side of the stackopposite said rods.
 4. A filter as defined in claim 1, wherein eachsheet has a tab and a notch along its periphery which are angularlyspaced so as not to be diametrically opposed, and wherein said housinghas a longitudinal rib and a longitudinal groove for mating with therespective notches and tabs of said sheets. 5 A filter as defined inclaim 4, wherein said rib is formed of a second longitudinal groove insaid housing confronting the notches in said sheets and an index rodextending through the opening defined by said second longitudinal grooveand said confronting notches.
 6. A filter comprising: a stack ofsubstantially identical flexible metal sheets, each sheet beingetch-roughened on one surface and with a pattern of projections on saidone surface; a housing for said stack; a body having inlet and outletports at one end to admit fluid into said body and through which fluidpasses out of said body; means positioning said housing in said bodywith one end of the stack adjacent said one end of said body, saidhousing having openings therein to permit fluid entering said body topass laterally between said sheets into the center openings thereof,said body having a passageway through which fluid entering said centeropenings passes out of said outlet port; a pair of rigid washers at eachend of said stack, one of said washers abutting one end of said housing;a first nut engaging the other washer and threaded into said housing forcompressing said sheets; a second nut threaded into said housing forlocking said first nut in place; a locking disc threaded into said bodyfor locking said housing therein; and passages interconnecting theopposite surfaces of said nuts and said disc with said inlet port forequalizing pressures therebetween.
 7. A filter cartridge for use in afilter housing placed in the path of a fluid containing particles to betrapped, said cartridge comprising: a stack of substantially identicalflexible metal sheets, each sheet having one roughened surface and aplurality of spaced projections in a prescribed pattern integral withsaid surface, the lateral surface portions of said projections beingminutely roughened; a housing for said stack; means for compressing saidsheets in said housing to make a rigid stack, whereby to permit saidstack to resist vibration, and whereby said pattern of projections andsaid roughened surfaces serve to trap particles in a fluid that flowsbetween said sheets.
 8. A filter as defined in claim 7, wherein saidmeans for compressing said sheets includes a member supported in saidhousing and having passages interconnecting its opposite surfaces forpressure equalization.